Currently there are hybrid vehicles that utilize regenerative braking to convert wasted energy from braking into electrical energy by means of a generator. Also, highway cruising can be made more efficient by pulling excess power from the motor or wheels and converting it to electric energy. Hybrid vehicles are very expensive and may never save as much money in gas as they cost to procure. Also, many people already have a vehicle and they can't afford to upgrade to a hybrid vehicle whenever gas prices get overly expensive.